The present invention relates to an aircraft flight surface actuator and a flight surface actuator system including such an actuator.
Modern aircraft have flight surfaces, such as the wings and tail section, that includes sections that are movable with respect to the rest of the flight surface. An example of this are the flaps in the trailing or leading edge of an aircraft wing. During takeoff and landing the flaps are deployed to increase the lift generated by the wing, the deployed flaps altering the overall shape of the wing and thus changing the lift generated by it.
Generally, the available space within an aircraft wing for housing the actuators used to move the flaps is not large as the leading and trailing edges of the wing tend to the thinnest points of the wing. Furthermore, the space within the wing is also used to house other mechanical systems, as well as for fuel storage.
Additionally mechanical forces exerted on the flaps, and thus the actuators, can be large and it is desirable to distribute these forces as evenly and widely across the flaps and structural elements of the wing as possible. It is therefore sometimes desirable to use a large number of actuators, so that no single actuator or associated wing section must withstand a particularly high load.
For the reason stated above it is therefore beneficial to have compact flight surface actuators.
According to a first aspect of the invention there is provided an aircraft flight surface actuator comprising at least one eccentric cam mechanism having an eccentric cam co-operating with a lever assembly, the lever assembly being coupled to a flight surface, whereby rotation of the eccentric cam imparts movement of the flight surface.
Preferably, the actuator further comprises a drive mechanism arranged to rotationally drive the or each eccentric cam mechanism. The drive mechanism may include a gear box of any suitable kind, being arranged to receive rotary drive from a power drive unit and to perform the appropriate speed reduction or multiplication to be imparted to the eccentric cam mechanism as appropriate.
Preferably, rotational drive from the gear arrangement is transmitted to the eccentric cam mechanism by means of a torque tube.
A number of eccentric cam mechanisms may receive rotational drive from a single gear arrangement, with each of the individual eccentric cam mechanisms being rotationally coupled to a neighboring cam mechanism by means of a torque tube, such a rotational drive from the gear arrangement is transmitted to each of the eccentric cam mechanisms.
Preferably, the lever assembly comprises a link element in engagement with the eccentric cam and a lever arm pivotally connected to the link element. Preferably, at least one of the pivotal connection between the lever arm and link element and the engagement means between the link element and eccentric cam comprise either a rolling element bearing, a plain bearing, a spherical plain bearing or a spherical rolling element bearing. The use of one of the listed bearings allows some degree of axial misalignment between the respective parts of the lever assembly. Such axial misalignment is likely to occur due to the loadings being applied to the flight control surfaces. For example, it would be appreciated by those skilled in the art that an aircraft wing is manufactured to accommodate a certain degree of flexing along its length and the use of such bearings accommodate this flexing without degradation of the performance of the bearing.
Preferably, the eccentric cam mechanism is arranged such that during movement of the cam mechanism and lever assembly across the full extent of their permitted travel the eccentric cam undergoes rotation of 180xc2x0. Additionally, the actuator is arranged such that at either extent of the maximum permitted movement of the cam mechanism and lever assembly the pivot point between the lever arm and link element and the pivot point about which the eccentric cam rotates coincide with a line of symmetry of the eccentric cam, whereby substantially zero torque can be transmitted from the link element to the eccentric cam. This particular feature of the eccentric cam means that it is not possible for the flight surface to which the actuator is connected to back drive the cam mechanism, as the link element is effectively latched at either extent of its maximum permitted travel.
According to a second aspect of the present invention there is provided a flight surface actuator system comprises a plurality of aircraft flight surface actuators according to the first aspect of the present invention, each aircraft flight surface actuator being rotationally coupled to a power drive unit.
Preferably, the power drive unit is connected to the gear arrangement of each of the plurality of flight surface actuators by means of a power transmission shaft. Additionally, the power transmission shaft is arranged to be concentric with the torque tubes coupled between each eccentric cam mechanism.